48 
SILUEIA. 
[Chap. III. 
fered with by igneous rocks, are observed to succeed each other with the 
utmost regularity, all having the same strike and dip as the Stiper Stones 
on which they rest. Of these transverse sections, that of Mytton Dingle 
is certainly the most expressive ; for, in addition to the great depth of this 
combe, its northern side presents a series of lofty-pinnacled rocks, the beds 
dipping symmetrically under each other to the W.N.W., through a thick- 
ness of not less than 3000 feet. 
The points nearest to the Stiper Stones at which fossils have been col- 
lected, along the western face of the ridge, are on the slopes of Lord's Hill, 
near the adjacent Chapel, and at the heads of the combes called Mytton 
Dingle and Perkins' Beech. They are still more abundant, and the species 
more varied, in the dark, almost black, earthy slates that overlie these 
flagstones and form the rising ground to the east of the Bog Mine. The 
same beds are richly fossiliferous a little further south at Bitton Castle, 
at the mining ground of Cefn-y-Gwynlle to the west of the southern 
termination of the Stiper Stones, called Heathmont, and at Disgwylfa 
near Snead. Similar fossils occur, and have been for some time known, 
in undulations of the same strata considerably to the west — as at the "White 
Grit Mines. 
Regarding all these localities as belonging to one and the same zone, 
the organic remains exhibited in the following woodcut are its dominant 
forms. They all have a true Lower Silurian fades. 
Fossils (9). From the West Side or the Stiper Stones. 
1. Obolella plumbea, Salter. 2. Eedonia anglica, id. 3. Eibeiria cornplanata, id. 
4. Orthoceras Avelinii, id. 5. Theca simplex, id. 6. iEglina binodosa, id. 7. Tri- 
nucleus Murchisonii, id. 8. Didymograpsus geminus, Hisinger. 9. Encrinite stem 
(the oldest known). 10. Orthoceras encrinale, Salter. 
In enumerating these fossils in the last edition, some valuable additions 
were made to the few forms previously described. Thus to the Illaenus 
perovalis of the ' Silurian System ' (PI. 23. f. 7), and the very charac- 
teristic species, Ogygia Selwynii (Foss. 10. f. 8), were added a new species 
of Trinucleus, T. Murchisonii (Foss. 9. f. 7), and the very remarkable 
iEglina, called M. binodosa (f. 6), from its invariably presenting a double 
tubercle on its third body-segment. Among the mollusks, the com- 
monest species is an Obolella, apparently special to this metalliferous 
